The invention relates to controls for conditioned air distribution systems, and in particular relates to a pneumatic controller having versatility for four different modes of operation to accommodate differing system operating parameters and components.
A great variety of controls, including pneumatic controls, have been disclosed and used previous to the present invention. For example, see U.S. Pat. Nos. 3,806,027; 3,934,795; 4,077,567; and 4,291,832, all assigned to the assignee of the present invention. These patents disclose systems and controllers involving various differing parameters in different conditioned air distribution systems, and the disclosures of these patents are hereby incorporated by reference into this application. Typical parameters which may vary in such systems are:
(1) whether the system is cooling or heating; PA0 (2) whether a spring-biased damper or flow valve in a duct of the system is normally open or normally closed (which determines whether the controller must be direct acting or reverse acting, respectively, as those terms are understood herein); PA0 (3) whether a thermostat connected to a controller is direct acting or reverse acting and PA0 (4) whether the controller is in a direct reset mode or a reverse reset mode, which is related to the type of thermostat used.
The above-listed U.S. Pat. No. 4,077,567 discloses and illustrates a pneumatic temperature reset differential pressure controller which functions in a general sense in the manner of the present invention. That velocity controller, for a variable air volume control system, was connectable to sensors for static air and total air in a duct, for sensing air flow velocity, and was reset by changes in the room air temperature as determined by a thermostat in the room. The controller included a means for full time on-line control of the air flow velocity in the variable air volume system, not simply acting as a maximum velocity limiter.
In the subject prior controller the room temperature signal from the thermostat was interlocked with a bias spring in a differential pressure controlled valve, to reset a velocity set point with changes in the room thermostat signal so that, for example, if the room became too hot, the differential pressure threshold (velocity threshold) at which a normally open duct damper would begin to be closed would be increased, tending to increase or to maintain at a maximum the cooling air flowing into the room.
In such a controller the interlock between the room temperature signal and the velocity set point or threshold enables the velocity controller to maintain a constantly regulated flow of air into a room in proportion to the room thermostat's demands and independently of variations of static pressure in the duct, since the sensors always measure pressure differential between the flowing air and static pressure. Such a velocity controller is a full time controller, not simply a maximum flow limiter or high limit controller, and the amount of air flow through the duct is controlled from near-zero flow to maximum flow (as set on the controller) in response to the signal from the thermostat. As in U.S. Pat. No. 4,077,567, such a system may include an adjustable minimum flow velocity mechanism for maintaining a regulated minimum amount of air into the room (provided the system source is delivering such a minimum velocity of air through the particular duct), regardless of whether the room thermostat is calling for any air.
In such systems the velocity pressure is generally sensed across a sensing diaphragm which is exposed to the total pressure (including the duct air velocity) on one side and to the static duct pressure on the other side, so that the difference in pressures across the sensing diaphragm corresponds to the air velocity only.
The above-referenced U.S. Pat. No. 4,077,567 has operated as an effective full time velocity controller, but it was designed to be limited to a specific situation, being solely a direct acting, direct reset controller. In other words, the controller was for use with a normally open damper actuator, and normally did not admit compressed air to a damper actuator line. Only when differential pressure between total air and static air exceeded a preset value did the diaphragm valve of the patented system shift to pressure to the actuator line to thereby inhibit air velocity in the duct by tending to close the normally open damper. The controller was for use in a cooling system with a direct acting thermostat, wherein higher temperature would cause pressurized air to flow through an outlet line from the thermostat to the reset portion of the controller, or in a heating system with a reverse acting thermostat.
In general, prior pneumatic controllers have not had the versatility of the present invention, for adjustment and reconfiguration to four different modes of operation depending on the particular system in which the controller is used and the damper and thermostat types employed in the system.
A pneumatic controller manufactured by Kreuter Mfg. Co. and marketed by Environment Elements Corp. under the trademark TITUS, one model of which is Model No. ESV 3010, has been capable of functioning in four different modes. However, that controller had a number of internal differential pressure actuated diaphragm valves, and instead of the versatility and easy reconfiguration of the present invention, the TITUS system depended upon repositioning and interchanging of input tubes among a number of different ports, and a complex system of air passages and a complex system of valves for switching among the passages to activate different modes of operation. In addition, the described controller had many internal smaller-than-pinhole-sized orifices for the flow of air, and the controller required a constant flow of air through it. Such orifices are easily clogged by small particles in moving air.
It is therefore an important object of the present invention to provide a pneumatic controller which controls velocity flow of air in a variable air volume distribution system in response to preset limits and in response to a thermostat as in U.S. Pat. No. 4,077,567, and also which has versatility for use in different systems with different operating parameters and components.